In the past, as rubber with an excellent oil resistance, heat resistance, and ozone resistance, a nitrile-group containing highly saturated copolymer rubber (also called “highly saturated nitrile rubber”, hydrogenated nitrile rubber included) has been known. Its cross-linked rubber is being used as materials for belts, hoses, gaskets, packings, oil seals, and various other automotive use rubber products. However, due to the increasingly smaller size and higher output of automobile engines, rubber materials more superior in heat resistance have become sought. Further, when using highly saturated nitrile rubber for seal applications, further reduction in compression set becomes necessary.
In the face of these circumstances, Patent Document 1 proposes a cross-linkable rubber composition containing highly saturated nitrile rubber having α,β-ethylenically unsaturated dicarboxylic acid monoester monomer units, a polyamine-based cross-linking agent and basic cross-linking accelerator. While this composition gives cross-linked rubber improved in heat resistance and compression set to a certain extent, further improvement of the compression set while maintaining the heat resistance in a good state has been sought.
Patent Document 1: Japanese Patent Publication (A) No. 2001-55471